C517A Datasheet, PDF (38/67 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

C517A
For clarification some terms regarding the difference between “baud rate clock” and “baud rate”
should be mentioned. In the asynchronous modes the serial interfaces require a clock rate which is
16 times the baud rate for internal synchronization. Therefore, the baud rate generators/timers have
to provide a “baud rate clock” (output signal in figure 17 and figure 18) to the serial interface which -
there divided by 16 - results in the actual “baud rate”. Further, the abbreviation f_OSC refers to the
oscillator frequency (crystal or external clock operation).
The variable baud rates for modes 1 and 3 of the serial interface 0 can be derived from either timer 1
or a dedicated baud rate generator (see figure 17). The variable baud rates for modes A and B of
the serial interface 1 are derived from a dedicated baud rate generator as shown in figure 18.
Timer 1 Overflow
f _OSC /2
Baud
Rate
Generator
(S0RELH
S0RELL)
ADCON0.7
(BD)
0
1
Mode 1
Mode 3
Mode 2
S0CON.7
S0CON.6
(SM0/
SM1)
Mode 0
PCON.7
(SMOD)
÷2
0
1
Only one mode
÷6
can be selected
Note : The switch configuration shows the reset state.
Figure 17
Serial Interface 0 : Baud Rate Generation Configuration
Baud
Rate
Clock
MCS03329
Baud Rate Generator
S1RELH .1 .0
S1RELL
f_OSC /2 _{Input Clock}
10-Bit Timer
Owerflow
MCS03331
Baud
Rate
Clock
Figure 18
Serial Interface 1 : Baud Rate Generator Configuration
The baud rate generator block in figure 17 has the same structure (10-bit auto-reload timer) as the
baud rate generator block which is shown in detail in figure 18.
Semiconductor Group
38
1997-10-01